Early automatic firearms relied on simple springs and used the gun's recoil to extract and then load another round.
In some high powered automatic firearms, a gas-operated long, short or direct piston has been used as a safe method to unlock the firearm's empty cartridge extraction mechanism. This is often referred to as “stroke piston action.” In these gas-operated piston designs, the bolt controlling the extraction mechanism is usually mechanically locked within the firearm's receiver. Upon firing, after a short delay, the rearward movement of a piston, acted upon by the pressure of propellant gases from the barrel will unlock and move the bolt to facilitate the extraction of the empty cartridge.
To properly extract and eject an empty cartridge from an automatic high powered rifle with a long, short, or direct stroke piston action, an elaborate locking mechanism is often necessary to bring about the slight delay, necessary for safety, after the round has been fired. In such firearms, although pressure from propellant gases is involved in the mechanism of activating empty cartridge extraction, such pressure from propellant gases is not also involved in the delaying of empty cartridge extraction. Rather, mechanical means are used to delay empty cartridge extraction.
Alternatively, with the development of high-powered rifle cartridges, gunsmiths have also attempted to use a system sometimes referred to as the “gas-delayed system”. This system employs the propellant gases from the exploded cartridge to trigger a locking mechanism to delay the cartridge's extraction. Such a gas-delayed system allows for the pressure in the barrel to return to ambient before empty cartridge extraction is activated. In such “gas-delayed system” firearms, the pressure from propellant gases has only been used in the mechanism of delaying the start of empty cartridge extraction. It has not been used to also activate empty cartridge extraction in such “gas-delayed system” firearms. It is often the case in these firearms that only the bolt's inertia is used to activate empty cartridge extraction.